A novel stimulus embedded in a sequence of repeated stimuli is often perceived to be longer in duration. Studies have indicated the involvement of repetition suppression in this duration distortion, but it remains unclear which processing stages are important. The present study examined whether high-level visual category processing contributes to the oddball's duration distortion. In Experiment 1, we presented a novel face image in either human, monkey, or cat category after a repetition of an identical human face image in the temporal oddball paradigm. We found that the duration distortion of the last stimulus increased when the face changed across different categories, than when it changed within the same category. However, the effect of category change disappeared when globally scrambled and locally scrambled face images were used in Experiments 2 and 3, respectively, suggesting that the difference in duration distortion cannot be attributed to low-level visual properties of the images. Furthermore, in Experiment 4, we again used intact face images and found that category changes can influence the duration distortion even when a series of different human faces was presented before the last stimulus. These findings indicate that high-level visual category processing plays an important role in the duration distortion of oddballs. This study supports the idea that visual processing at higher visual stages is involved in duration perception.
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